/*
 * Copyright 2007 the original author or authors.
 * 
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * 
 *      http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.wamblee.system.core;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Set;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.wamblee.collections.CollectionFilter;
import org.wamblee.conditions.Condition;
import org.wamblee.general.Pair;

/**
 * Container consisting of multiple components.
 * 
 * @author Erik Brakkee
 */
public class Container extends AbstractComponent<Scope> {

    private static final Log LOG = LogFactory.getLog(Container.class);

    private List<Component> _components;
    private Set<String> _componentNames;
    private CompositeInterfaceRestriction _restriction; 
    private boolean _sealed;
   
    static ProvidedInterface[] filterProvidedServices(
            Component aClient, RequiredInterface aRequired, Collection<Pair<ProvidedInterface,Component>> aProvided,
            InterfaceRestriction aRestriction) {
        List<ProvidedInterface> result = new ArrayList<ProvidedInterface>();
        for (Pair<ProvidedInterface,Component> descriptor : aProvided) {
            ProvidedInterface provided = descriptor.getFirst();
            Component server = descriptor.getSecond();
            if (aRequired.implementedBy(provided) && 
                    !aRestriction.isViolated(aClient, aRequired, server, provided)) {
                result.add(provided);
            }
        }
        return result.toArray(new ProvidedInterface[0]);
    }

    /**
     * Constructs the container
     * 
     * @param aName
     *            Name of the container
     * @param aComponents
     *            Components.
     * @param aProvided
     *            Provided services of the container
     * @param aRequired
     *            Required services by the container.
     */
    public Container(String aName, Component[] aComponents,
            ProvidedInterface[] aProvided, RequiredInterface[] aRequired) {
        super(aName, aProvided, aRequired);
        _components = new ArrayList<Component>();

        _componentNames = new HashSet<String>();
        _restriction = new CompositeInterfaceRestriction();
        _sealed = false;
        for (Component component : aComponents) {
            addComponent(component);
        }
    }

    public Container(String aName) {
        this(aName, new Component[0], new ProvidedInterface[0],
                new RequiredInterface[0]);
    }

    public Container addComponent(Component aComponent) {
        checkSealed();
        if (aComponent.getContext() != null) {
            throw new SystemAssemblyException(
                    "Inconsistent hierarchy, component '"
                            + aComponent.getName()
                            + "' is already part of another hierarchy");
        }
        if (_componentNames.contains(aComponent.getName())) {
            throw new SystemAssemblyException("Duplicate component '"
                    + aComponent.getName() + "'");
        }
        _components.add(aComponent);
        _componentNames.add(aComponent.getName());
        aComponent.addContext(getQualifiedName());
        return this;
    }
    
    /**
     * Adds an interface restriction for explicitly configuring the 
     * relations between components. 
     * @param aRestriction Restriction to add. 
     * @return Reference to this to allow call chaining. 
     */
    public Container addRestriction(InterfaceRestriction aRestriction) {
        checkSealed(); 
        _restriction.add(aRestriction);
        return this; 
    }

    @Override
    public Container addProvidedInterface(ProvidedInterface aProvided) {
        checkSealed();
        super.addProvidedInterface(aProvided);
        return this;
    }

    @Override
    public Container addRequiredInterface(RequiredInterface aRequired) {
        checkSealed();
        super.addRequiredInterface(aRequired);
        return this;
    }

    /**
     * Validates the components together to check that there are no required
     * services not in the required list and no services in the provided list
     * that cannot be provided. Also logs a warning in case of superfluous
     * requirements.
     * 
     * @throws SystemAssemblyException
     *             in case of any validation problems.
     */
    public void validate() {
        validateProvidedInterfacesArePresent();

        validateRequiredInterfaces();

        doStartOptionalDryRun(null, true);
    }

    private void validateRequiredInterfaces() {
        List<RequiredInterface> required = new ArrayList<RequiredInterface>();
        for (Component component : _components) {
            required.addAll(Arrays.asList(component.getRequiredInterfaces()));
        }

        for (RequiredInterface service : getRequiredInterfaces()) {
            // TODO required interfaces by the component could be
            // subclasses or implementations of the requirements
            // of the contained components. The code below assumes
            // an exact match.
            if (!(required.contains(service))) {
                info("Service '"
                        + service
                        + "' indicated as required is not actually required by any of the components");
            }
            // Check for the case that the externally required service
            // is optional whereas the internally required service is
            // mandatory.
            if (service.isOptional()) {
                for (RequiredInterface intf : required) {
                    if (intf.equals(service) && !intf.isOptional()) {
                        warn("Required service '"
                                + service
                                + "' indicated as optional is mandatory by one of its components ("
                                + getClients(intf)
                                + ", "
                                + intf
                                + "), this can lead to problems when the container is started and the interface is not provided to the container.");
                    }
                }
            }
        }
    }

    private void validateProvidedInterfacesArePresent() {
        List<ProvidedInterface> provided = new ArrayList<ProvidedInterface>();
        for (Component component : _components) {
            provided.addAll(Arrays.asList(component.getProvidedInterfaces()));
        }
        for (ProvidedInterface service : getProvidedInterfaces()) {
            // TODO provided interfaces by components could be
            // provide subclasses or implementations of the
            // provided interfaces of the container.
            // The code below assumes an exact match.
            if (!(provided.contains(service))) {
                throw new SystemAssemblyException(getName() + ": Service '"
                        + service
                        + "' is not provided by any of its components");
            }
        }
    }

    /**
     * Starts the container. After the container is started, the container
     * becomes sealed meaning that no further components, required or provided
     * interfaces may be added.
     * 
     * @return Scope.
     */
    public Scope start() {
        checkSealed();
        validate();
        Scope scope = super.start(new DefaultScope(new ProvidedInterface[0]));
        seal();
        return scope;
    }

    /**
     * Seal the container, meaning that no further components or interfaces may
     * be added.
     */
    public void seal() {
        _sealed = true;
    }

    /**
     * Checks if the container is sealed.
     * 
     * @return True iff the container is sealed.
     */
    public boolean isSealed() {
        return _sealed;
    }

    @Override
    protected Scope doStart(Scope aExternalScope) {
        return doStartOptionalDryRun(aExternalScope, false);
    }

    private Scope doStartOptionalDryRun(Scope aExternalScope, boolean aDryRun) {
        LOG.info("Starting '" + getQualifiedName() + "'");

        Scope scope = new DefaultScope(getProvidedInterfaces(), aExternalScope);

        List<Pair<ProvidedInterface,Component>> allProvided = new ArrayList<Pair<ProvidedInterface,Component>>();
        
        addProvidersOfRequiredInterfaces(allProvided);

        List<Component> started = new ArrayList<Component>();
        for (Component component : _components) {
            try {
                initializeProvidersForRequiredInterfaces(allProvided,
                        component, aDryRun);

                // Start the service.
                if (!aDryRun) {
                    Object runtime = component.start(scope);
                    scope.addRuntime(component, runtime);
                    started.add(component);
                }

                // add all provided services
                ProvidedInterface[] provided = component
                        .getProvidedInterfaces();
                for (ProvidedInterface prov: provided) { 
                    allProvided.add(new Pair<ProvidedInterface,Component>(prov, component));
                }
            } catch (SystemAssemblyException e) {
                throw e;
            } catch (RuntimeException e) {
                LOG.error(getQualifiedName() + ": could not start '"
                        + component.getQualifiedName() + "'", e);
                stopAlreadyStartedComponents(started, scope);
                throw e;
            }
        }
        return scope;
    }

    private void addProvidersOfRequiredInterfaces(
            List<Pair<ProvidedInterface,Component>> allProvided) {
        // all interfaces from the required list of this container are
        // provided to the components inside it.
        RequiredInterface[] required = getRequiredInterfaces();
        for (RequiredInterface intf : required) {
            ProvidedInterface provider = intf.getProvider();
            if (provider != null) {
                allProvided.add(new Pair<ProvidedInterface,Component>(provider, null));
            } else {
                if (!intf.isOptional()) {
                    throw new SystemAssemblyException(getQualifiedName()
                            + ": required interface '" + intf
                            + "' is not provided");
                }
            }
        }
    }

    private void stopAlreadyStartedComponents(List<Component> aStarted,
            Scope aScope) {
        // an exception occurred, stop the successfully started
        // components
        for (int i = aStarted.size() - 1; i >= 0; i--) {
            try {
                Component component = aStarted.get(i);
                aStarted.get(i).stop(aScope.getRuntime(component));
            } catch (Throwable t) {
                LOG.error(getQualifiedName() + ": error stopping "
                        + aStarted.get(i).getQualifiedName());
            }
        }
    }

    /**
     * Sets the provided interface or a component.
     * 
     * @param aAllProvided
     *            All available provided interfaces.
     * @param aComponent
     *            Component whose required interfaces we are looking at.
     * @param aValidateOnly
     *            If true then the provider will not be set for required
     *            interfaces.
     */
    private void initializeProvidersForRequiredInterfaces(
            List<Pair<ProvidedInterface,Component>> aAllProvided, Component aComponent,
            boolean aValidateOnly) {
        // Check if all required services are already provided by
        // earlier
        // systems.

        for (RequiredInterface descriptor : aComponent.getRequiredInterfaces()) {
            ProvidedInterface[] filtered = filterProvidedServices(aComponent, descriptor,
                    aAllProvided, _restriction);
            if (filtered.length == 1) {
                if (!aValidateOnly) {
                    descriptor.setProvider(filtered[0]);
                }
            } else if (filtered.length > 1) {
                throw new SystemAssemblyException(
                        "Service '"
                                + descriptor
                                + "' required by system '"
                                + aComponent
                                + "' matches multiple services provided by other systems: "
                                + getServers(filtered));
            } else {
                // filtered.length == 0
                if (!descriptor.isOptional()) {
                    throw new SystemAssemblyException(
                            "Service '"
                                    + descriptor
                                    + "' required by system '"
                                    + aComponent
                                    + "' is not provided by systems that are started earlier");
                }
            }
        }
    }

    @Override
    protected void doStop(Scope aScope) {
        for (int i = _components.size() - 1; i >= 0; i--) {
            Component component = _components.get(i);
            Object runtime = aScope.getRuntime(component);
            component.stop(runtime);
        }
    }

    private void info(String aMsg) {
        LOG.info(getQualifiedName() + ": " + aMsg);
    }

    private void warn(String aMsg) {
        LOG.warn(getQualifiedName() + ": " + aMsg);
    }

    private String getServers(ProvidedInterface[] aProvidedList) {
        String result = "";
        for (ProvidedInterface provided : aProvidedList) {
            result += "(components ";
            for (Component component : _components) {
                for (ProvidedInterface provided2 : component
                        .getProvidedInterfaces()) {
                    if (provided.equals(provided2)) {
                        result += component + " ";
                    }
                }
            }
            result += ", interface " + provided + ")";
        }
        return result;
    }

    private List<Component> getClients(RequiredInterface aRequirement) {
        List<Component> clients = new ArrayList<Component>();
        for (Component component : _components) {
            for (RequiredInterface required : component.getRequiredInterfaces()) {
                if (required.equals(aRequirement)
                        && required.isOptional() == aRequirement.isOptional()) {
                    clients.add(component);
                }
            }
        }
        return clients;
    }

    private void checkSealed() {
        if (_sealed) {
            throw new SystemAssemblyException("Container is sealed");
        }
    }
}